Shareholders will get $38.25 in cash plus units of an Atlas pipeline affiliate, for a total of $43.34 a share, a 37 percent premium to yesterday’s closing price, Atlas said in a statement today. The company, based in Moon Township, Pennsylvania, had its largest one-day share gain since it began trading in 2004.

The deal is worth $4.3 billion including assumed debt, the companies said. If completed, the purchase would be the third- largest for San Ramon, California-based Chevron and its biggest since the 2005 acquisition of Unocal Corp.

Atlas “has one of the premier acreage positions in the prolific Marcellus,” George L. Kirkland, Chevron vice chairman, said in a statement. “The high quality resource, competitive cost structure in the Marcellus, strong growth potential of the asset base and its proximity to premier natural-gas markets make this targeted acquisition a compelling investment for Chevron.”

The Marcellus Shale stretches from Pennsylvania into New York, West Virginia and Ohio and may hold 262 trillion cubic feet of natural gas, making it the largest known U.S. gas field, according to Energy Department estimates. Marcellus gas has averaged 11 percent more than the benchmark price over the past year, because wells are closer to East Coast population centers.

Atlas rose $10.84, or 34 percent, to $42.56 at 10:33 a.m. on the Nasdaq Stock Market. Chevron fell 90 cents, or 1.1 percent, to $83.90 in New York Stock Exchange composite trading.

Shale Production

The planned purchase follows the June 28 acquisition of shale-gas producer XTO Energy Inc. by Exxon Mobil Corp., the largest U.S. energy company, for $34.9 billion. BP Plc, Total SA, Statoil ASA and Royal Dutch Shell Plc also have purchased U.S. shale assets to increase reserves and output, betting that gas prices will rise as economic recovery boosts energy demand.

In addition to acreage, companies are adding expertise in shale production, which involves drilling horizontally for thousands of feet, then fracturing the shale-rock formations with injections of water, sand and chemicals. The U.S. Environmental Protection Agency is studying the effects hydraulic fracturing may have on water supplies and the environment.

Producers expect so-called tight formations on other continents to be exploited for oil and gas. Chevron said the Atlas purchase complements its recent shale-gas deals in Poland, Romania and Canada.

Reliance Agreement

Atlas reported more than 1 trillion cubic feet of natural gas reserves at the end of last year and controls 622,000 acres in the Marcellus Shale, according to its website. The company reported today that daily output for the third quarter rose 18 percent from a year earlier to the equivalent of 118.3 million cubic feet.

Chevron said it will assume Atlas Energy’s role in a $1.7 billion agreement announced in April with India’s Reliance Industries Ltd. to produce gas from the Marcellus Shale. In that agreement, Reliance paid $340 million upfront and agreed to pay up to $1.36 billion of its partner’s drilling cost, in addition to its own.

The premium for today’s deal is more than the 13 percent average for the 253 U.S. oil and gas acquisitions announced this year, according to Bloomberg data. Chevron is paying 14 times profit before interest, taxes, depreciation and amortization for Atlas, compared with an average of 11 times for the four largest oil and gas deals announced this year.

Other Buyers?

“I wouldn’t be surprised to see another buyer emerge,” said Scott Hanold, a Houston-based analyst for RBC Capital Markets. “This values the company at about $9,000 an acre for a Marcellus position. Reliance paid about $14,000 an acre for the joint venture in Atlas’s core holdings. Investors are going to want some more.”

Hanold rates Atlas Energy a buy and doesn’t own the shares.

Atlas Pipeline Holdings LP will buy producing oil and gas assets from Atlas Energy for $30 million in cash and $220 million in newly issued units, the partnership said in a separate statement. After the transaction, Atlas Energy will no longer control the partnership.

Atlas Energy will buy a 49 percent stake in Laurel Mountain Midstream LLC, a pipeline system in western Pennsylvania, for $403 million in cash from another affiliate, Atlas Pipeline Partners LP, according to a statement. Williams Partners LP, the pipeline owner controlled by Tulsa, Oklahoma-based Williams Cos., is the majority owner and operator of the Laurel Mountain system.

Jefferies Group Inc. is acting as lead financial adviser and Deutsche Bank AG is serving as co-financial adviser to Atlas Energy. Wachtell, Lipton, Rosen & Katz is legal adviser to Atlas Energy.

Goldman Sachs Group Inc. is serving as financial adviser to Chevron and Skadden Arps Slate Meagher & Flom LLP is its legal adviser.